High-moisture extrusion process of transglutaminase-modified peanut protein: Effect of transglutaminase on the mechanics of the process forming a fibrous structure

At present, the quality of the peanut protein-based meat substitutes developed by high-moisture extrusion process still cannot fully meet the consumers’ requirements from the aspect of the fiber strength. In this study, the peanut protein was modified by the transglutaminase (TGase) and then extruded under a high moisture condition (55%). Effect of TGase on the mechanics of the process forming a fibrous structure were investigated. Results showed that during the high-moisture extrusion process, the TGase can improve the sensory properties by affecting the layered structure forming speed of peanut protein, but excessive TGase (more than 0.2%) would accelerate the cross-linking, which was not conducive to the rearrangement of protein molecules and the improvement of the fibrous structure. In the extruder barrel, TGase can promote the unfolding, aggregating, and cross-linking of the disorderly arranged protein molecular chains, and help to break the hydrogen bonds and disulfide bonds, but enhance the hydrophobic interactions. Moreover, the TGase made the arachin molecular chains more flexible, which was beneficial to the subsequent rearrangement. In the die, during the rearrangement of the protein molecules, the addition of 0.1% or 0.2% TGase can promote to form new hydrogen bonds and disulfide bonds to stabilize the protein conformation. From the cooling zone to the extrudate, the TGase was beneficial to the stretching of protein molecular chains and would promote to synthesize the larger protein subunits (66 kDa). Under the effect of TGase, the main forces maintaining the fibrous structure were converted into the hydrophobic interactions, hydrogen bonds, and disulfide bonds. At the same time, after modified by the TGase, the proportion of four protein secondary structures was presented as β-sheet > α-helix > β-turn > random coil structure. Therefore, the mechanism of the process for forming a fibrous structure of peanut protein with different aggregation degree modified by TGase has been clarified, which will be helpful for improving the quality of peanut protein-based meat substitutes.